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US20070013443A1 - Compartmental gain limiter and controlling method thereof - Google Patents

Compartmental gain limiter and controlling method thereof Download PDF

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Publication number
US20070013443A1
US20070013443A1 US11/483,631 US48363106A US2007013443A1 US 20070013443 A1 US20070013443 A1 US 20070013443A1 US 48363106 A US48363106 A US 48363106A US 2007013443 A1 US2007013443 A1 US 2007013443A1
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Prior art keywords
resistor
amplifier
compartmental
terminal
signal
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US11/483,631
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English (en)
Inventor
Chih-Hui Tien
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Asustek Computer Inc
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Asustek Computer Inc
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Assigned to ASUSTEK COMPUTER INC. reassignment ASUSTEK COMPUTER INC. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: TIEN, CHIH-HUI
Publication of US20070013443A1 publication Critical patent/US20070013443A1/en
Abandoned legal-status Critical Current

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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
    • H03F3/181—Low-frequency amplifiers, e.g. audio preamplifiers
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
    • H03F1/08—Modifications of amplifiers to reduce detrimental influences of internal impedances of amplifying elements
    • H03F1/12—Modifications of amplifiers to reduce detrimental influences of internal impedances of amplifying elements by use of attenuating means
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
    • H03F1/52—Circuit arrangements for protecting such amplifiers
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03G—CONTROL OF AMPLIFICATION
    • H03G7/00—Volume compression or expansion in amplifiers
    • H03G7/002—Volume compression or expansion in amplifiers in untuned or low-frequency amplifiers, e.g. audio amplifiers
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F2200/00—Indexing scheme relating to amplifiers
    • H03F2200/441—Protection of an amplifier being implemented by clamping means
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F2200/00—Indexing scheme relating to amplifiers
    • H03F2200/78—A comparator being used in a controlling circuit of an amplifier

Definitions

  • the invention relates in general to a compartmental gain limiter and a controlling method thereof, and more particularly to a compartmental gain limiter for an audio amplifier and a controlling method thereof.
  • the personal computer, the video disc player, or the notebook computer often serve as a video/audio player, and the user also expects the personal computer, the video disc player or the notebook computer serving as the video/audio player to have a better video/audio playing effect.
  • the speaker in the current notebook computer has the specification of 8 ⁇ /1W, and the maximum with standing input voltage is 2.828Vrms (the maximum voltage is 4V), which is higher than the output power of the typical mobile player.
  • the power connected to the audio amplifier of the notebook computer is 5V, so the voltage outputted to the speaker may exceed 4V and thus burns out the speaker.
  • the engineer reduces the voltage gain of the audio amplifier so as to prevent the speaker from burning out.
  • the voltage gain is reduced, the actual output power of the audio is insufficient. For example, even if the volume of the speaker of the notebook computer is adjusted to the maximum, the shock effect generated by the mobile player still cannot be obtained.
  • FIG. 1A is a circuit diagram showing an inverting amplifier in a conventional audio amplifier.
  • an inverting amplifier 100 includes an OP amplifier 110 , a resistor R 1 and a resistor R 2 .
  • An external power 160 provides a DC operation voltage Vcc for the OP amplifier 110 .
  • the gain value of the inverting amplifier is - R ⁇ ⁇ 2 R ⁇ ⁇ 1 .
  • FIG. 1B is a circuit diagram showing a noninverting amplifier in the conventional audio amplifier.
  • a noninverting amplifier 200 includes an OP amplifier 110 , a resistor R 3 , a resistor R 4 , a resistor R 5 and a resistor R 6 .
  • An external power 160 provides a DC operation voltage Vcc for the OP amplifier 110 .
  • the gain value of the noninverting amplifier is R ⁇ ⁇ 5 R ⁇ ⁇ 5 + R ⁇ ⁇ 6 ⁇ R ⁇ ⁇ 3 + R ⁇ ⁇ 4 R ⁇ ⁇ 3 .
  • the maximum amplitudes of the AC output voltage V 1 ′ of the inverting amplifier 100 ( FIG. 1A ) and the AC output voltage V 2 ′ of the noninverting amplifier 200 ( FIG. 1B ) are determined according to the DC operation voltage Vcc of the OP amplifier 110 , and the AC output voltages V 1 ′ ( FIG. 1A ) and V 2 ′ ( FIG. 1B ) have to be applied to a speaker 190 such that the acoustic effect can be generated. So, it is to be particularly noted that whether the amplitude of the AC output voltage V 1 ′ or V 2 ′ exceeds the loading of the speaker 190 or not.
  • the speaker used in the notebook computer typically has the specification of 8 ⁇ /1W, so the peak-to-peak value (Vp-p) of the AC output voltage V 1 ′ or V 2 ′ that can be withstood by the speaker 190 is about 4V. Furthermore, the DC operation voltage provided in the notebook computer is 5V. So, when the AC output voltage V 1 ′ or V 2 ′ generated after the AC input voltage V 1 or V 2 is amplified is greater than 4V, the speaker 190 tends to burn out because it cannot withstand the loading.
  • the gain value of the audio amplifier or the AC input voltage of the audio amplifier has to be reduced according to a maximum amplitude Vomax of the AC output voltage that can be withstood by the speaker 190 , such that the amplitude of the AC output voltage V 1 ′ or V 2 ′ is clamped.
  • Vomax the maximum amplitude of the AC output voltage that can be withstood by the speaker 190
  • the original output volume of the speaker 190 is sacrificed, and the overall acoustic effect is reduced.
  • FIG. 2A is a circuit diagram showing the inverting amplifier with an added DC voltage transformer.
  • FIG. 2B is a circuit diagram showing the noninverting amplifier with an added DC voltage transformer.
  • another method for clamping the amplitudes of the AC output voltages V 1 ′ and V 2 ′ of the OP amplifier 110 is to reduce the DC operation voltage Vcc of the OP amplifier 110 in order to prevent the speaker 190 from burning out and to make the DC operation voltage Vcc equal the maximum amplitude Vomax of the AC output voltage that can be withstood by the speaker 190 .
  • the object of clamping the amplitude of the AC output voltage of the OP amplifier 110 may be achieved by adding a DC voltage transformer 170 to adjust the voltage of the external power 160 to be equal to the maximum amplitude Vomax of the AC output voltage that can be withstood by the speaker 190 .
  • adding the DC voltage transformer 170 has to enlarge the area of the printed circuit board and thus increase the manufacturing cost.
  • the added DC voltage transformer 170 occupies the space in the original system, and EMI (Electro Magnetic Interference) may occur to interfere with the normal operation of the electronic product.
  • EMI Electro Magnetic Interference
  • the compartmental gain limiter of the invention can amplify an AC input voltage according to an original gain value of an audio amplifier and then output an AC output voltage when an amplitude of the AC output voltage of the audio amplifier does not reach a maximum amplitude of the AC output voltage, which can be withstood by a speaker.
  • the actual audio output power can make the speaker keep the original sound field shock effect.
  • the compartmental gain limiter clamps the AC input voltage or the gain value of the audio amplifier so as to protect the speaker from burning out by the too-high AC output voltage.
  • the invention achieves the above-identified object by providing a compartmental gain limiter to be connected to an audio amplifier, which has a gain value and outputs an output signal according to an input signal and the gain value.
  • the compartmental gain limiter includes a comparator and a clamper.
  • the comparator has a critical value.
  • the comparator detects the output signal of the audio amplifier, and outputs a driven signal when the output signal of the audio amplifier is greater than the critical value of the comparator.
  • the clamper receives the driven signal and outputs a control signal, according to the driven signal, to control the audio amplifier to clamp the output signal.
  • the invention also achieves the above-identified object by providing a method of controlling a compartmental gain limiter, which is connected to an audio amplifier.
  • the compartmental gain limiter includes a comparator and a clamper.
  • the method includes the steps of: utilizing the comparator to detect an output signal of the audio amplifier; judging whether the output signal is greater than a critical value of the comparator; outputting a driven signal when the output signal is greater than the critical value; driving the clamper to output a control signal according to the driven signal; and controlling the audio amplifier to clamp the output signal according to the control signal.
  • FIG. 1A is a circuit diagram showing an inverting amplifier in a conventional audio amplifier.
  • FIG. 1B is a circuit diagram showing a noninverting amplifier in the conventional audio amplifier.
  • FIG. 2A is a circuit diagram showing the inverting amplifier with an added DC voltage transformer.
  • FIG. 2B is a circuit diagram showing the noninverting amplifier with an added DC voltage transformer.
  • FIG. 3 is a block diagram showing a compartmental gain limiter of the invention, which is connected to an audio amplifier.
  • FIG. 4A is a schematic illustration showing a compartmental gain limiter connected to an inverting amplifier according to a first embodiment of the invention.
  • FIG. 4B is a schematic illustration showing a compartmental gain limiter connected to an inverting amplifier according to a second embodiment of the invention.
  • FIG. 4C is a schematic illustration showing a compartmental gain limiter connected to an inverting amplifier according to a third embodiment of the invention.
  • FIG. 5A is a schematic illustration showing a compartmental gain limiter connected to an inverting amplifier according to a fourth embodiment of the invention.
  • FIG. 5B is a schematic illustration showing a compartmental gain limiter connected to an inverting amplifier according to a fifth embodiment of the invention.
  • FIG. 5C is a schematic illustration showing a compartmental gain limiter connected to an inverting amplifier according to a sixth embodiment of the invention.
  • FIG. 6A is a schematic illustration showing a compartmental gain limiter connected to a noninverting amplifier according to a seventh embodiment of the invention.
  • FIG. 6B is a schematic illustration showing a compartmental gain limiter connected to a noninverting amplifier according to an eighth embodiment of the invention.
  • FIG. 6C is a schematic illustration showing a compartmental gain limiter connected to a noninverting amplifier according to a ninth embodiment of the invention.
  • FIG. 7A is a schematic illustration showing a compartmental gain limiter connected to a noninverting amplifier according to a tenth embodiment of the invention.
  • FIG. 7B is a schematic illustration showing a compartmental gain limiter connected to a noninverting amplifier according to an eleventh embodiment of the invention.
  • FIG. 7C is a schematic illustration showing a compartmental gain limiter connected to a noninverting amplifier according to a twelfth embodiment of the invention.
  • FIG. 8 is a circuit diagram showing a compartmental gain limiter connected to an inverting amplifier according to a thirteenth embodiment of the invention.
  • FIG. 9A shows measured waveforms when an AC output voltage of the conventional inverting amplifier does not reach a critical value.
  • FIG. 9B shows measured waveforms when an AC output voltage of the invention does not reach a critical value.
  • FIG. 9C shows measured waveforms when the AC output voltage of the conventional inverting amplifier exceeds the critical value.
  • FIG. 9D shows measured waveforms when the AC output voltage of the invention exceeds the critical value.
  • FIG. 10 is a flow chart showing a method of the compartmental gain limiter for controlling the audio amplifier according to a preferred embodiment of the invention.
  • FIG. 3 is a block diagram showing a compartmental gain limiter of the invention, which is connected to an audio amplifier.
  • a compartmental gain limiter 300 is connected to an audio amplifier 310 , which may be, for example, an inverting amplifier or a noninverting amplifier.
  • the audio amplifier 310 amplifies an input signal S 1 according to a gain value and then outputs an output signal S 2 .
  • the compartmental gain limiter 300 includes a comparator 330 and a clamper 320 .
  • the comparator 330 receives the output signal S 2 of the audio amplifier 310 . When the output signal S 2 of the audio amplifier 310 is greater than a critical value of the comparator 330 , the comparator 330 outputs a driven signal S 4 .
  • the clamper 320 outputs a control signal S 5 according to the driven signal S 4 of the comparator 330 .
  • the compartmental gain limiter 300 controls the input signal S 1 or the gain value of audio amplifier 310 according to the control signal S 5 so as to clamp the output signal S 2 of the audio amplifier 310 .
  • the problems of decreasing the overall output power and influencing the original sound field shock effect of a speaker which occur in the conventional audio amplifier when the original voltage gain of the audio amplifier 310 is sacrificed in order to prevent the speaker from burning out, may be effectively solved.
  • FIG. 4A is a schematic illustration showing a compartmental gain limiter connected to an inverting amplifier according to a first embodiment of the invention.
  • the audio amplifier is an inverting amplifier 400 in one embodiment.
  • the inverting amplifier 400 includes a resistor R 7 a , a resistor R 7 b , a resistor R 8 and an OP amplifier 410 .
  • a second terminal of the resistor R 7 a is electrically connected to a first terminal of the resistor R 7 b .
  • a second terminal of the resistor R 7 b and a first terminal of the resistor R 8 are electrically connected to an inverting input terminal of the OP amplifier 410 .
  • a second terminal of the resistor R 8 is electrically connected to an output terminal of the OP amplifier 410 .
  • a noninverting input terminal of the OP amplifier 410 is grounded.
  • the gain value of the inverting amplifier 400 is determined according to the resistor R 7 a , the resistor R 7 b and the resistor R
  • the inverting amplifier 400 When an input signal of the inverting amplifier 400 is an AC input voltage V 3 and enters the inverting amplifier 400 through the first terminal of the resistor R 7 a , the inverting amplifier 400 amplifies the AC input voltage V 3 according to the gain value and then outputs an output signal, such as an AC output voltage V 3 ′, to the comparator 330 of the compartmental gain limiter 300 .
  • the critical value of the comparator 330 may be a reference voltage Vref.
  • the comparator 330 When the AC output voltage V 3 ′ is greater than the reference voltage Vref, the comparator 330 outputs a driven signal S 4 .
  • the clamper 320 outputs a control signal S 5 according to the driven signal S 4 so as to control the voltage of the inverting input terminal of the OP amplifier 410 and thus to clamp the AC output voltage V 3 ′.
  • the output signal received by the comparator 330 of the compartmental gain limiter 300 may be the AC output voltage V 3 ′ or the potential difference between two terminals of the resistor R 8 , for example.
  • FIG. 4B is a schematic illustration showing a compartmental gain limiter connected to an inverting amplifier according to a second embodiment of the invention.
  • the comparator 330 of the compartmental gain limiter 300 compares the potential difference between the two terminals of the resistor R 8 with the reference voltage (not shown) of the comparator 330 .
  • the comparator 330 outputs a driven signal S 4 .
  • the clamper 320 outputs a control signal S 5 according to the driven signal S 4 so as to control the voltage of the inverting input terminal of the OP amplifier 410 and thus to clamp the AC output voltage V 3 ′.
  • FIG. 4C is a schematic illustration showing a compartmental gain limiter connected to an inverting amplifier according to a third embodiment of the invention.
  • the output signal may also be the potential difference between two terminals of the resistor R 7 b .
  • the comparator 330 of the compartmental gain limiter 300 compares the potential difference between the two terminals of the resistor R 7 b with the reference voltage Vref. When the potential difference between the two terminals of the resistor R 7 b is greater than the reference voltage Vref, the comparator 330 outputs a driven signal S 4 .
  • the clamper 320 outputs a control signal S 5 according to the driven signal S 4 so as to control the voltage of the inverting input terminal of the OP amplifier 410 and thus to clamp the AC output voltage V 3 ′.
  • the clamper 320 of the compartmental gain limiter 300 outputs a control signal S 5 according to the driven signal S 4 .
  • the control signal S 5 of the clamper 320 can control the voltage of the inverting input terminal of the OP amplifier 410 .
  • the clamper 320 may also be configured such that the clamper 320 can change the resistance of the resistor R 8 according to the control signal S 5 so as to control the gain value of the inverting amplifier 400 .
  • FIG. 5A is a schematic illustration showing a compartmental gain limiter connected to an inverting amplifier according to a fourth embodiment of the invention. Referring to FIG.
  • the comparator 330 of the compartmental gain limiter 300 compares the output signal of the inverting amplifier 400 with the reference voltage Vref, wherein the output signal may be, for example, the AC output voltage V 3 ′.
  • the comparator 330 outputs a driven signal S 4 .
  • the clamper 320 outputs a control signal S 5 according to the driven signal S 4 .
  • the clamper 320 changes the resistance of the resistor R 8 according to the control signal S 5 so as to control the gain value of the inverting amplifier 400 and thus to clamp the AC output voltage V 3 ′.
  • the output signal received by the comparator 330 of the compartmental gain limiter 300 may be the AC output voltage V 3 ′ or the potential difference between two terminals of the resistor R 8 .
  • FIG. 5B is a schematic illustration showing a compartmental gain limiter connected to an inverting amplifier according to a fifth embodiment of the invention.
  • the comparator 330 compares the potential difference between the two terminals of the resistor R 8 with the reference voltage (not shown in FIG. 5B ) of the comparator 330 .
  • the comparator 330 outputs a driven signal S 4 .
  • the clamper 320 outputs a control signal S 5 according to the driven signal S 4 .
  • the clamper 320 changes the resistance of the resistor R 8 according to the control signal S 5 so as to control the gain value of the inverting amplifier 400 and thus to clamp the AC output voltage V 3 ′.
  • FIG. 5C is a schematic illustration showing a compartmental gain limiter connected to an inverting amplifier according to a sixth embodiment of the invention.
  • the output signal may also be the potential difference between two terminals of the resistor R 7 .
  • the comparator 330 of the compartmental gain limiter 300 may also compare the potential difference between the two terminals of the resistor R 7 with the reference voltage (not shown) of the comparator 330 . When the potential difference between the two terminals of the resistor R 7 is greater than the reference voltage, the comparator 330 outputs a driven signal S 4 .
  • the clamper 320 outputs a control signal S 5 according to the driven signal S 4 .
  • the clamper 320 changes the resistance of the resistor R 8 according to the control signal S 5 so as to control the gain value of the inverting amplifier 400 and thus to clamp the AC output voltage V 3 ′.
  • FIG. 6A is a schematic illustration showing a compartmental gain limiter connected to a noninverting amplifier according to a seventh embodiment of the invention.
  • the audio amplifier may be a noninverting amplifier 600 .
  • the noninverting amplifier 600 includes a resistor R 9 , a resistor R 10 , a resistor R 11 , a resistor R 12 and an OP amplifier 610 .
  • the second terminal of the resistor R 12 and the first terminal of the resistor R 11 are electrically connected to the noninverting input terminal of the OP amplifier 610 .
  • the second terminal of the resistor R 11 is grounded.
  • the first terminal of the resistor R 9 and the first terminal of the resistor R 10 are electrically connected to the inverting input terminal of the OP amplifier 610 .
  • the second terminal of the resistor R 9 is grounded.
  • the second terminal of the resistor R 10 is electrically connected to the output terminal of the OP amplifier 610 .
  • the gain value of the noninverting amplifier 600 is determined according to the resistor R 9 , the resistor R 10 , the resistor R 11 and the resistor R 12 .
  • the noninverting amplifier 600 When the input signal of the noninverting amplifier 600 is an AC input voltage V 4 and enters the noninverting amplifier 600 through the first terminal of the resistor R 12 , the noninverting amplifier 600 amplifies the AC input voltage V 4 according to the gain value and then outputs an output signal to the comparator 330 .
  • the output signal may be, for example, an AC output voltage V 4 ′.
  • the critical value of the comparator 330 may be a reference voltage Vref.
  • the comparator 330 When the AC output voltage V 4 ′ is greater than the reference voltage Vref, the comparator 330 outputs a driven signal S 4 .
  • the clamper 320 outputs a control signal S 5 according to the driven signal S 4 so as to control the voltages between two terminals of the resistor R 11 and thus to clamp the AC output voltage V 4 ′.
  • the output signal received by the comparator 330 of the compartmental gain limiter 300 may be an AC output voltage V 4 ′ or a potential difference between two terminals of the resistor R 10 .
  • FIG. 6B is a schematic illustration showing a compartmental gain limiter connected to a noninverting amplifier according to an eighth embodiment of the invention.
  • a comparator 330 of the compartmental gain limiter 300 compares the potential difference between the two terminals of the resistor R 10 with the reference voltage (not shown). When the potential difference between the two terminals of the resistor R 10 is greater than the reference voltage, the comparator 330 outputs a driven signal S 4 .
  • the clamper 320 outputs a control signal S 5 according to driven signal S 4 so as to control the voltages between the two terminals of the resistor R 11 and thus to clamp AC output voltage V 4 ′.
  • FIG. 6C is a schematic illustration showing a compartmental gain limiter connected to a noninverting amplifier according to a ninth embodiment of the invention.
  • the output signal may also be the potential difference between two terminals of the resistor R 9 .
  • the comparator 330 may also compare the potential difference between the two terminals of the resistor R 9 with the reference voltage Vref. When the potential difference between the two terminals of the resistor R 9 is greater than the reference voltage Vref, the comparator 330 outputs a driven signal S 4 .
  • the clamper 320 outputs a control signal S 5 according to the driven signal S 4 so as to control the voltages between the two terminals of the resistor R 11 and thus to clamp the AC output voltage V 4 ′.
  • the clamper 320 of the compartmental gain limiter 300 outputs a control signal S 5 according to the driven signal S 4 so as to control the voltages between the two terminals of the resistor R 10 .
  • the clamper 320 may also be configured such that the clamper 320 can change the resistance of the resistor R 10 according to the control signal S 5 so as to control the gain value of the noninverting amplifier 600 .
  • FIG. 7A is a schematic illustration showing a compartmental gain limiter connected to a noninverting amplifier according to a tenth embodiment of the invention. Referring to FIG.
  • the comparator 330 of the compartmental gain limiter 300 compares the output signal of the noninverting amplifier 600 with the reference voltage Vref, wherein the output signal may be the AC output voltage V 4 ′, for example.
  • the comparator 330 outputs a driven signal S 4 .
  • the clamper 320 of the compartmental gain limiter 300 outputs a control signal S 5 according to the driven signal S 4 .
  • the clamper 320 can change the resistance of the resistor R 10 according to the control signal S 5 so as to control the gain value of the noninverting amplifier 600 and thus to clamp the AC output voltage V 4 ′.
  • the output signal received by the comparator 330 may be the AC output voltage V 4 ′ or the potential difference between two terminals of the resistor R 10 , for example.
  • FIG. 7B is a schematic illustration showing a compartmental gain limiter connected to a noninverting amplifier according to an eleventh embodiment of the invention. Referring to FIG. 7B , the comparator 330 compares the potential difference between the two terminals of the resistor R 10 with the reference voltage (not shown) of the comparator 330 . When the potential difference between the two terminals of the resistor R 10 is greater than the reference voltage, the comparator 330 outputs a driven signal S 4 . The clamper 320 outputs a control signal S 5 according to the driven signal S 4 . The clamper 320 can change the resistance of the resistor R 10 according to the control signal S 5 so as to control the gain value of the noninverting amplifier 600 and thus to clamp the AC output voltage V 4 ′.
  • FIG. 7C is a schematic illustration showing a compartmental gain limiter connected to a noninverting amplifier according to a twelfth embodiment of the invention.
  • the output signal may also be the potential difference between two terminals of the resistor R 9 , for example.
  • the comparator 330 of the compartmental gain limiter 300 may also compare the potential difference between the two terminals of the resistor R 9 with the reference voltage (not shown) of the comparator 330 . When the potential difference between the two terminals of the resistor R 9 is greater than the reference voltage, the comparator 330 outputs a driven signal S 4 .
  • the clamper 320 outputs a control signal S 5 according to the driven signal S 4 .
  • the clamper 320 can change the resistance of the resistor R 10 according to the control signal S 5 so as to control the gain value of the noninverting amplifier 600 and thus to clamp the AC output voltage V 3 ′.
  • FIG. 8 is a circuit diagram showing a compartmental gain limiter connected to an inverting amplifier according to a thirteenth embodiment of the invention.
  • the circuit of the thirteenth embodiment includes an OP amplifier 710 , a resistor R 13 , a resistor Rf 1 , a resistor Rf 2 , a resistor Rf 3 , a first transistor Q 1 and a second transistor Q 2 .
  • This embodiment utilizes the cut-in voltage at the base-emitter junction of the first transistor Q 1 and the second transistor Q 2 as a reference voltage of the comparator 330 , and utilizes the voltages of the collector and the emitter of the first transistor Q 1 and the second transistor Q 2 as the clamper 320 .
  • the resistor Rf 1 and the resistor Rf 3 have substantially the same resistance so that the outputs of the first transistor Q 1 and the second transistor Q 2 are clamped when the positive half cycle and the negative half cycle of the AC output voltage exceed the reference voltage.
  • the second terminal of the resistor R 13 , the first terminal of the resistor Rf 1 , the emitter of the first transistor Q 1 and the collector of the second transistor Q 2 are electrically connected to the inverting input terminal of the OP amplifier 710 .
  • the second terminal of the resistor Rf 1 and the first terminal of the resistor Rf 2 are electrically connected to the base of the first transistor Q 1 .
  • the second terminal of the resistor Rf 2 and the first terminal of the resistor Rf 3 are electrically connected to the base of the second transistor Q 2 .
  • the second terminal of the resistor Rf 3 , the collector of the first transistor Q 1 and the emitter of the second transistor Q 2 are electrically connected to the output terminal of the OP amplifier.
  • the noninverting input terminal of the OP amplifier 710 is grounded.
  • the circuit determines the AC output voltage V 3 ′ according to the current flowing through the resistor and the resistances of the resistor Rf 1 , the resistor Rf 2 and the resistor Rf 3 .
  • the circuit of the embodiment can clamp the AC output voltage according the cut-in voltage at the base-emitter junction of the transistor.
  • This embodiment can have the function of temperature compensation according to the property that the cut-in voltage at the base-emitter junction of the transistor is inversely proportional to the temperature.
  • the invention does not intend to limit itself to the usage of the transistor to achieve the function of the comparator. Instead, the function of this embodiment may be achieved according to the circuit layout of the OP amplifier.
  • FIG. 9A shows measured waveforms when an AC output voltage of the conventional inverting amplifier does not reach a critical value.
  • FIG. 9B shows measured waveforms when an AC output voltage of the invention does not reach a critical value.
  • the AC output voltage of the invention and the AC output voltage of the conventional inverting amplifier are amplified according to the original gain value of the inverting amplifier and then outputted.
  • FIG. 9C shows measured waveforms when the AC output voltage of the conventional inverting amplifier exceeds the critical value.
  • FIG. 9D shows measured waveforms when the AC output voltage of the invention exceeds the critical value.
  • the conventional inverting amplifier still amplifies the AC input voltage according to the original gain value and the speaker cannot withstand the too-great load and burns out.
  • the invention clamps the AC output voltage within the loading range that can be withstood by the speaker so as to protect the speaker from burning out.
  • FIG. 10 is a flow chart showing a method of the compartmental gain limiter for controlling the audio amplifier according to a preferred embodiment of the invention.
  • the method of controlling the compartmental gain limiter includes the following steps. First, step 11 utilizes the comparator to detect the output signal of the audio amplifier. Then, step 12 judges whether the output signal is greater than the critical value of the comparator. Next, step 13 outputs the driven signal when the output signal is greater than the critical value. Then, step 14 drives the clamper to output the control signal according to the driven signal. Finally, step 15 controls the audio amplifier to clamp the output signal according to the control signal.
  • the input signal that does not reach the critical value is amplified according to the gain value of the audio amplifier and then an output signal is outputted to maintain the original sound field effect.
  • the gain value or the input signal of the audio amplifier is reduced in order to protect the speaker from burning out due to the too-large output signal.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Multimedia (AREA)
  • Control Of Amplification And Gain Control (AREA)
  • Tone Control, Compression And Expansion, Limiting Amplitude (AREA)
US11/483,631 2005-07-15 2006-07-11 Compartmental gain limiter and controlling method thereof Abandoned US20070013443A1 (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116165471A (zh) * 2023-04-20 2023-05-26 泉州昆泰芯微电子科技有限公司 一种信号过载监测系统、监测方法及可编程增益放大器

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